This invention relates to a hoist arrangement for a dragline rigging.
Conventional dragline riggings include a hoist arrangement which is connectable to a dragline bucket for hoisting the bucket during excavation. The known hoist arrangements generally comprise a pair of lower hoist chains which are connectable to trunnions on the side walls of the bucket, a spreader bar above the bucket to hold the lower hoist chains away from the bucket side walls during hoisting so as to prevent these chains from damaging the side walls, and a pair of upper hoist chains connected at lower ends to the spreader bar and at upper ends to a pick-up link on the dragline rigging. Typically, the lower and upper hoist chains are formed from an abrasive-resistant steel and are oversized to account for wear during operation. The spreader bar is also formed from steel and together with the lower and tipper hoist chains tends to be relatively heavy.
Although conventional hoist arrangements are durable, the total mass which the dragline boom has to carry when the dragline bucket is hoisted includes the mass of the hoist arrangement, and it is therefore desirable to have a hoist arrangement with a relatively low mass so that the loading capacity of the dragline bucket itself, and hence the efficiency of the dragline, can be increased.
According to the invention there is provided a hoist arrangement for a dragline rigging comprising:
a pair of lower hoist members which are attachable to trunnions on a dragline bucket; and
an upper hoist member in the form of a triangular framework formed at least predominantly from fibreglass, the triangular framework including first attachment formations for attachment to the lower hoist members so as to hold these members apart from one another and at least one second attachment formation for attachment to a pick-up link on the dragline rigging.
In a preferred embodiment of the invention, the upper hoist member includes a hollow fibreglass spreader bar and two fibreglass ties which are attachable to the spreader bar.
The spreader bar may include steel inserts which are arranged to receive replaceable bushes or sealed bearing units for attaching the spreader bar to the fibreglass ties and to the lower hoist members. Similarly, the fibreglass ties may include steel inserts which are designed to carry replaceable bushes or sealed bearing units for attaching the ties to the spreader bar and to the pick-up link.
In another embodiment, the spreader bar is secured to the fibreglass ties with bolts and the triangular framework includes a series of swivel bearings for attaching the framework to the lower hoist members and to the pick-up link.
The lower hoist members may comprise at least two wire-reinforced, synthetic rubber belts, and may include an abrasive-resistant cover.
Typically, the hoist belts are attached to steel connectors for connecting the belts to the spreader bar and to the trunnions on the dragline bucket.
In another arrangement, the lower hoist members comprise two endless slings each of which includes a portion which is cast into a polyurethane connector for connecting the sling to one of the trunnions on the dragline bucket.